1. Field of the Invention
The present invention relates to a motor.
2. Description of the Related Art
In recent years, various components and mechanisms used in a vehicle have been developed with a specific focus on environmental concerns (e.g., energy efficiency, reduction of carbon dioxide emission, and the like). One of such mechanisms is an “idling stop” mechanism which allows an engine of a vehicle not in motion to automatically stop in order to reduce the carbon dioxide emission.
However, when a compressor is activated by the engine of such vehicle, each time the engine stops the components activated by the compressor, such as an air conditioner, also stop. In order to avoid such inconvenience, the compressor of the components, such as an air conditioner, is operated by a motor (e.g., IPM (Interior Permanent Magnet)). That is, the compressor is activated by a car battery, which allows the air conditioner to continue to operate even while the engine is not running.
Generally, when the rpm of a motor increases, the voltage (i.e., back electromotive force) induced by the coil in the motor also increase. When such voltage equals the voltage of the drive power source, the increase of the rpm stops, that is, the rpm is compromised. The motor used in the vehicle needs to run on a relatively low powered car battery while a wide range of rpm is required. Therefore, in order to increase the rpm of the motor, some technologies have been developed.
For example, the international publication No. WO 2004/010562 discloses a technology (flux weakening control) to increase the rpm of a motor.
However, according to the technology disclosed above, when each coil in a stator includes a plurality of teeth (i.e., distributed winding), the efficiency of the flux weakening control varies depending on the rotational angle of a rotor core. In particular, when an entire magnetic pole of the rotor core is arranged opposite to a coil of the stator, the degree of the reduction of the magnetic flux becomes great, and when a portion of the magnetic pole of the rotor core is arranged opposite to the coil of the stator, the degree of the reduction of the magnetic flux becomes small.
As described above, when the degree of the reduction of the entire magnetic flux is varied depending on the rotational angle of the rotor angle, the rpm of the motor will be compromised.